FIG. 8 illustrates a state of a conventional fluid coupling whose plug 101 and socket 102 are separated from each other, FIGS. 9A and 9B illustrate a state in which the plug 101 and the socket 102 are connected with each other, and FIG. 10 illustrates a state in which the plug 101 is pulled away from the socket 102.
As illustrated in FIG. 8, a socket-side flow path is formed between an inner surface of the socket 102 and a fixed valve 103 which is fixed at an inside of the socket 102. A socket-side seal 105, which is disposed at a seal guide 104, is biased by a guide spring 106 so as to be pressed against the fixed valve 103, and the seal guide 104 is abutted against the inner surface of the socket 102 via a first seal ring 107, so that the socket-side flow path is closed. Steel balls 109, which are housed in holes 108 for locking the steel balls of the socket 102, are restricted to move inward by a guide ring 111 which is biased by a guide ring spring 110.
In the plug 101, a plug-side seal 116 is disposed at a distal end of a movable valve 115 which is disposed via a valve guide 114 so as to be movable in axial directions. This plug-side seal 116 is pressed against a valve seat 117 of the plug 101 by a valve spring 118 so that the plug-side flow path is closed.
When the plug 101 is inserted into the socket 102, first, the distal end of the plug 101 and the socket-side seal 105 are abutted with each other so as to seal the plug 101 and the socket 102 with each other. Then, when the distal end of the plug 101 is further pressed inward into the socket 102 while the movable valve 115 is being slid on the inner surface of the valve guide 114 and moved backward against the biasing force of the valve spring 118, the socket-side seal 105 moves in a direction of arrow A against the biasing force of the guide spring 106. With this, the press contact between the socket-side seal 105 and the fixed valve 103, and the press contact between the plug-side seal 116 and the valve seat 117 are released so that the socket-side flow path and the plug-side flow path are connected with each other. Simultaneously, a stepped portion 119, which is disposed at an outer circumferential surface of the plug 101, moves the guide ring 111 in the direction of arrow A so that the steel balls 109 are inserted into a locking groove 120 of the plug 101 so as to be locked. As mentioned above, the plug 101 and the socket 102 are locked with each other without requiring an operation of a sleeve 124 when the plug 101 is mounted, improving its operability. At this time, as illustrated in FIG. 9B, the seal guide 104 and the socket 102 are sealed by the first seal ring 107 of the socket 102 at a portion adjacent to an abutment portion between the socket-side seal 105 and the distal end of the plug 101. Moreover, the plug 101 and the socket 102 are sealed by a second seal ring 123.
In order to release a combined state between the plug 101 and the socket 102 illustrated in FIG. 9A, the sleeve 124 of the socket 102 is moved in the A direction so as to retract the steel balls 109 from the locking groove 120. Then, when the plug 101 is pulled in a direction opposite to the direction A, as illustrated in FIG. 10, the socket-side seal 105 is biased by the guide spring 106 and moves forward so as to be pressed against the fixed valve 103. With this, the socket-side flow path is closed. Moreover, when the plug 101 moves in the direction opposite to the direction A, the valve spring 118 biases the movable valve 115 so that the valve seat 117 and the plug-side seal 116 are pressed with each other so as to close the plug-side flow path. Then, the distal end of the plug 101 and the socket-side seal 105 are separated from each other so that the seal between the plug 101 and the socket 102 is released. In this fluid coupling, in order to minimize the remaining liquid at a connection space portion between the plug 101 and the socket 102 when the plug 101 is attached and detached, the distal end portions of the fixed valve 103 and the movable valve 115 are configured to be planar. The planar distal end portions are abutted with each other so as to minimize the space which is generated therebetween so that the remaining liquid, namely, the leakage of fluid, which is generated when the plug 101 is removed, is minimized.
However, in the above-mentioned conventional fluid coupling, as illustrated in FIG. 9B, the distance between the first seal ring 107 and the second seal ring 123 is long so that between the first seal ring 107 and the second seal ring 123 is generated a space S which is surrounded by the plug 101, the socket 102, the socket-side seal 105, and the seal guide 104. Moreover, the seal between the plug 101 and the socket 102 is established only by bringing the distal end of the plug 101 and the socket-side seal 105 into abutment. Therefore, when the plug 101 is inclined, the abutment between the plug 101 and the socket-side seal 105 is loosened so that leaked liquid accumulates in the space S. Accordingly, when the plug 101 is separated from the socket 102, the liquid, which has accumulated in the space S, leaks outside. Moreover, it is not assured that the flow paths of the plug 101 and the socket 102 are opened while ensuring the seal between the plug 101 and the socket 102. Accordingly, in some cases, the generation of remaining liquid cannot be avoided.
Furthermore, since the seal guide 104 and the guide ring 111 are disposed separately, the guide spring 106 and the guide ring spring 110 need to be disposed also separately. Accordingly, the number of parts increases, and its assembling requires a lot of time.
Then, there is proposed in Patent Document 1 a configuration which more surely ensures the seal between the plug and the socket. That is, in this fluid coupling, when the plug is inserted into the socket, the plug is inserted into a collar so as to press a movable valve body. Because the plug and the collar are fitted into each other, the seal between the plug and the socket is more surely established so as to prevent the liquid leakage.